This application pertains to the assembly of sheet metal duct work. More particularly, it pertains to a transverse joint technique for connecting abutting sections of sheet metal ducts.
Sheet metal ducts are generally designed to function in one of three situations. They may carry air in an external situation (e.g. rooftop) in which the duct work must be insulated. In such cases, at each transverse joint, it is necessary to seal the joint or else the positive air pressure within the duct work, escaping through the cracks at the joints will blow off the insulation surrounding the duct work and conditioned air may be lost. In order to seal the joints of such exterior duct work, it has become conventional to utilize a gasket material betwen the abutting edges or flanges of the duct sections, and then secure the connection with a relatively elaborate clamping system. Examples of such types of transverse joint connections are illustrated and described in U.S. Pat. Nos. 3,630,549 to Grimm and 3,791,681 to Moldow.
In a second environment for sheet metal duct work, the air carried through the duct work contains a product of some type therein, such as lint, waste, dust, grain, and the like. In such situations, it is preferable to have the joint relatively air tight so that the material being carried within the duct cannot escape. It is also highly preferable that the interior wall of the duct at the joint contain no protruding obstructions to the path of air and product flow therethrough. Otherwise, there will be encountered tagging, build up of product at the joint area, and/or turbulence within the duct work leading to loss of efficiency in air flow. One solution to this problem is the Lockformer system in which flanges are formed on the end of each duct section adjacent the joint, which flanges bend outwardly from the wall of the duct, then parallel to the duct in a direction away from the interface. A gasket is positioned between the abutting upstanding flanges. A separate connector surrounding the joint is bent around the shaped flanges to secure the joint. While this arrangement is satisfactory once it is accomplished, it is relatively heavy and too costly to use in the first situation described above. The cost is increased as a result of special equipment necessary to form the double flanges required, which equipment is not suitable for other uses. Further, the special corner connecting pieces are expensive.
In a third situation, sheet metal duct work is used to transport air in an interior situation such as within the walls of an industrial plant. In such environment, it is not necessary to obtain an absolute seal at each transverse joint because the duct is in the area to be air conditioned, and a small amount of leakage is not going to matter since the air is merely going to leak into the space to be conditioned. Therefore, here the emphasis is on ease of assembly and economy. A conventional joint for such types of installations is referred to as the pocket lock joint in which a clip is positioned on the raw edge of one of the duct sections, and then a special tool punches through the clip and the raw edge to form a fastener on one edge. The clip includes a portion that extends perpendicularly to the wall of the duct and then back longitudinally and receives an upstanding flange which is bent into the adjacent edge of the adjoining duct. Once the flange is inserted within the clip, the top portion is bent down over the flange to secure the second section to the first. While this is an effective, and relatively economical joint forming technique, it is only applicable to interior air conditioning ducts which are not to be insulated, which do not have to be sealed, and which are not carrying any product therein, because the punched portion of the clip and duct extends into the interior of the duct and would cause a severe tagging problem if a product were being carried through the duct.
In the present invention, the purpose is to provide one type of transverse joint system that can be used in all environments, and is also both relatively easy to assemble without special tools, and economical to produce. Toward this end, then, the joint of the present invention is effected, first of all, by each side wall of each of the duct sections being so preformed as to terminate in an integrally formed, outwardly extending flange. In each of such flanges, there is provided a plurality of laterally aligned, spaced tabs formed in the wall surface thereof. These tabs protrude outwardly from the surface of the flange in a direction away from the joint being formed. Finally, a generally V-shaped, snap-on coupling member clips onto each pair of opposed flanges and locks them together.
The V-shaped coupling member includes a pair of opposed walls connected along one edge, while a portion of the free edges of the walls are folded back between the walls to form a pair of retaining edges. As the coupling is snapped onto the flanges, the resilience in the folded metal member causes the walls to spring aside as the coupling member is pushed onto the flanges, then the retaining edges snap in behind the protruding tabs in the flanges to secure the coupling member thereon. It is apparent that the distance between the side wall of the duct and the point on the flange at which the tab is formed must be slightly greater than the width of the retaining edges.
The ends of the coupling members extend out laterally past the termination of the corresponding side wall. The ends of adjacent coupling members are then overlapped and secured in some suitable manner. In situations where sealing is required, a gasket is placed between the opposing flanges of the two duct sections prior to the installation of the coupling member.
It is, therefore, an object of the present invention to provide a sheet metal duct transverse joint system which is more economical to fabricate and may be assembled without special tools, yet may be utilized with exterior ducts, interior ducts, or ducts carrying product therein.
It is another object of the present invention to provide a sheet metal duct transverse joint of the type described in which the inside wall of the duct is smooth at the point of the connection, there being no protrusions or abutments extending within the duct work.
It is yet another object of the present invention to provide a transverse joint system of the type described which further includes a simple corner-connecting means for connecting the corners of the coupling members .